1. Field of the Invention
The present invention relates to a crawler, a crawler pin, a crawler bush or a crawler manufacturing method, which is to be used in a construction or civil engineering machine such as a excavator or a bulldozer.
2. Related Art
As shown in FIG. 17A, a crawler 50 of a construction machine is generally constructed to include: a crawler shoe 51; a pair of crawler links 52 and 53 fixed on the crawler shoe 51 by means of bolts; a crawler bush 54 press-fitted/fitted in the holes formed in the crawler links 52 and 53; and a crawler pin 55 inserted into the crawler bush 54 and press-fitted/fitted in the holes of the crawler links 52 and 53. As the toothed sprocket of a drive sprocket meshes with the crawler bush 54 press-fitted between the crawler links 52 and 53, the crawler 50 turns to run the construction machine. Between the end portions of the crawler bush 54 and the crawler pin 55, as shown in FIG. 17B, there are arranged seal devices 56 for preventing the soil and sand and the muddy water from coming into the clearance between the crawler bush 54 and the crawler pin 55 thereby to improve the wear lifetimes of the inner circumference of the crawler bush 54 and the outer circumference of the crawler pin 55.
Here, the aforementioned crawler bush is hardened at its inner and outer circumferences by the carburizing and quenching method or the induction-quenching method, as shown in FIGS. 18A to 18D. In FIG. 18A, for example, the inner and outer circumferences are induction-quenched to leave a soft layer at the end face, so that this type is used in a later-described dry type crawler. In FIG. 18B, the outer circumference is prominently deepened in its hardness to enlarge the hardened layer width from the outer circumference although the soft layer appears at the end face, so that this type is used in the later-described wet type crawler 50, too. In FIG. 18C, the inner and outer circumferences and the end face surfaces are continuously hardened by the carburizing and quenching method so that this type is used in the later-described wet type crawler, too. In FIG. 18D, after the entirety was hardened by quenching it, the inner circumference is induction-quenched to form a deep hardened layer on the outer circumference and on the surface of the end face, and a tempered soft layer leading to the inner circumference and a shallow inner circumference hardened layer are formed, so that this type is used in the later-described wet type crawler, too. In the crawler pin, moreover, the outer circumference is hardened by a similar heat treatment to improve the strength and the wear resistance of the crawler.
In the portions at the running drive sprocket and the idler wheel, on the other hand, rotations in the circumferential direction of the crawler bush 54 and the crawler pin 55 occur between the crawler bush 54 and the crawler pin 55 inserted into the inner circumference of the crawler bush 54, so that unusual noises (or uncomfortable sounds) such as creaks or seizure noises are easily made while the bush 54 and the pin 55 are sliding in contact (or in the sliding contact state). In order to prevent the crawler bush and the crawler pin from being lowered in strength by the unusual noises or the seizures, an adjustment is made to make the external diameter of the crawler pin smaller than the internal diameter of the crawler bush.
In the bulldozer to run at a high speed, moreover, there is used the wet type crawler which has lubricating oil confined between the crawler bush and the crawler pin, to suppress the aforementioned uncomfortable sounds and to prevent the seizure between the crawler pin and the crawler bush. However, this wet type crawler structure takes a high price. In the crawler such as one for the hydraulic shovel having little necessity for a high-speed run, therefore, there is generally used the dry type crawler which has no lubricating oil confined.
In the aforementioned construction machine, it is known that an extremely high unbalanced load acts on the crawler pin and the crawler bush of the crawler, no matter whether the crawler might be dry or wet. A load of the body weight (W) or higher frequently acts on a set of crawler pin and crawler bush, and the load may rise to three times (3W) or more when the construction machine rides over a hard obstacle.
At the portion, to which the unbalanced load is easily applied, the clearance between the crawler bush and the crawler pin is important. From the viewpoint of strength, it is preferred to narrow that clearance thereby to support the unbalanced load by both the crawler bush and the crawler pin. In case a slippage occurs between the crawler bush and the crawler pin, as described hereinbefore, there easily occurs the problem of seizure, namely, a breakage from the inner circumference of the crawler bush. With a larger clearance between the crawler bush and the crawler pin, moreover, the problem of the seizure is naturally lightened, but there arise other problems that the crawler bush is easily broken and that the crawler bush has to be more large-sized for reinforcing the crawler bush.
From these viewpoints, in most cases, the clearance between the crawler bush and the crawler pin is set between 0.4 to 1.2 mm in terms of the diametrical difference. In case the unbalanced load is raised when the excavator runs continuously on rough surfaces or when the bulldozer runs at a high speed, however, there arise problems that the seizure cannot be avoided, as schematically shown in FIG. 19, and that the crawler bush is frequently broken when the clearance between the two is large.
Especially, the contact portion by the unbalanced load takes a high bearing pressure and an extremely low sliding speed and is used under the reciprocating conditions. In the wet type crawler containing the lubricating oil, therefore, the seizure easily occurs, and the oil seal may be broken by the overheat to cause leakage of the lubricating oil. Another problem is that the crawler bush and the crawler pin are broken at the seized portion.
As a countermeasure for this seizure phenomenon, on the other hand, the crawler pin and the crawler bush are prominently hardened on their sliding faces by the induction-quenching method or the carburizing and quenching method. As another countermeasure, it is conceivable to coat the surface of the crawler pin and the inner circumference of the crawler bush with a phosphate film, a carbide, a nitride or a super-hard solid lubricant (e.g., MoS2 or graphite). However, it is difficult to form those surface improving layers thick (e.g., about 10 microns). This difficulty fails to lead to a sufficient improvement in the lifetime and causes another problem of a high cost.
In the wet type crawler containing the lubricating oil, on the other hand, an oil hole is formed in the crawler pin so that it can feed the lubricating oil preferentially to the positions, to which the unbalanced load is easily applied, as shown in FIG. 19. However, it deteriorates the crawler pin strength to form the oil hole at the positions of the maximum unbalanced load of the crawler pin. From the viewpoint of raising the strength of the crawler, an undesired problem is left such as breaking the crawler pin.
Here, Unexamined Published Japanese Patent Application No. 2001-88755 has been disclosed with a view to minimizing the wears of the inner circumference of the crawler bush and the outer circumference of the crawler pin, thereby to improve the durability and lifetime of the crawler even when the soil and sand come into the clearance between the crawler bush and the crawler pin. In this Application it has been disclosed to provide: 1) a crawler having a structure, in which a plurality of foreign substance trapping grooves extending axially while being circumferentially spaced are formed in the inner circumference of a crawler bush; 2) a crawler having a structure, in which a resin layer made of a hard resin material is formed on the inner circumference of a crawler bush and in which a plurality of foreign substance trapping grooves extending axially while being circumferentially spaced are formed in the resin layer; and 3) a crawler having a structure, in which sliding elements made of a hard resin material are disposed on the inner circumference of a crawler bush and in a plurality of foreign substance trapping grooves extending axially while being circumferentially spaced, so that a crawler pin is slidably supported by the sliding elements, and in which a plurality of space portions are formed between the inner circumference of the crawler bush and the outer circumference of the crawler pin while being circumferentially spaced.
In that Application, moreover, it has been disclosed to use an ultra-high-molecular-weight polyethylene resin excellent in the sliding characteristics as the aforementioned hard resin material and to fill and use the aforementioned plurality of foreign substance trapping grooves and space portions with grease for lubricating the clearance between the crawler bush and the crawler pin.
In the crawler bush which is provided with the plurality of foreign substance trapping grooves extending axially while being circumferentially spaced of the aforementioned crawler bush inner circumference, however, the trapping grooves are parallel to the progressing direction of the annularly crushing breakage of the crawler bush due to the aforementioned unbalanced load and are the sources for a serious stress concentration so that the breaking strength is extremely lowered.
In case a load of 1 W or higher is applied to one crawler bush, as described hereinbefore, the pressure to be applied to the hard resin layer of the crawler bush becomes excessive. This resin layer does not have sufficient hardness or strength so that the crawler bush cannot prevent its setting. The resin layer, as squeezed out by the setting, may deteriorate the sealability of the seal devices of the crawler. Moreover, the crawler bush is seriously worn under a high bearing pressure by the slippage from the crawler pin, and the resin layer itself hardly contributes to the improvement in the strength of the crawler bush, thereby to raise a problem that the strength of the crawler bush is lowered by the thickness of the resin layer. It is, therefore, desired to design a compact crawler while making the crawler bush as small as possible.
The present invention has been conceived in view of the problems thus far described and has an object to provide a crawler, a crawler pin, a crawler bush and a crawler manufacturing method, which can improve the lubrication between the crawler bush and the crawler pin without lowering the crawler strength at the running time, thereby to prevent the creak or seizure, as might otherwise be caused at the running time. More specifically, the object of the invention is to provide a crawler, a crawler pin, a crawler bush and a crawler manufacturing method, which are made silent and excellent in high strength and wear resistance, by arranging a metallic sliding member of an excellent wear resistance in the clearance formed between the crawler bush and the crawler pin to prevent the crawler bush through the metallic sliding member from being broken by the reaction from the crawler pin in sliding contact against the breaking stress on the inner circumference of the crawler bush at the running time, by preventing the creak and the seizure noise, as might otherwise be caused by the sliding contact between the crawler bush and the crawler pin at the running time, and by absorbing the hammering noise which is caused at the time of meshing with the sprocket.